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Eyepiece Recommendations

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#1 Guest_**DONOTDELETE**_*

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Posted 18 October 2005 - 11:02 AM

I'm looking for any recommendations for a low power eyepiece for an 8 inch LX200 telescope. What is the longest focal length eyepiece I can use? I have a Celestron Ultima 30mm now. Would I be better off getting a focal reducer instead of a lower power eyepeice? I have a 2 inch star diagonal so I can use any good 2 inch eyepieces as well.

#2 Mike B

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Posted 18 October 2005 - 11:55 AM

Hi Steve-
Welcome aboard! :grin:
Someone here turned me onto the 30mm BW Optik 2" EP with an 82* FOV... works great in my 10" F10 SCT. There's even a thread on it recently in this forum. Does same thing a FR would accomplish, so i'd much recommend it over the FR...
Sells for about $100. Check it out!
:cool: mike b

#3 Guest_**DONOTDELETE**_*

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Posted 18 October 2005 - 03:17 PM

Mike,

Thanks for the welcome and the tip! I guess what I'd most like to know is if I want to get the lowest power/widest true field of view look at the sky without vignetting, what's the longest focal length eyepiece I can use or should I use a field reducer instead? I'm guessing the that longest would be somewhere in the 35-40mm range. Are there any favorites out there?

#4 Guest_**DONOTDELETE**_*

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Posted 18 October 2005 - 03:35 PM

41mm televue panoptic.
I think this gives the largest true field in an 8" f/10 SCT.

#5 Lew Zealand

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Posted 18 October 2005 - 03:40 PM

The longest focal length EP you can use in an 8" SCT without noticeable vignetting will result in about 1.3° of visible sky, which include:

31mm 80-82° AFOV - 31mm Nagler or 30mm BW Optik/1rpd/Moonfish and other clones
38mm 68-70° AFOV - Meade, William Optics, Burgess, UO, and many others have EPs with similar specs.

There are others but I don't have 'em all memorized yet…

#6 Chris Schroeder

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Posted 18 October 2005 - 05:12 PM

GSO 42mm superview 65deg AFOV

#7 Burnim

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Posted 18 October 2005 - 05:41 PM

Check this out. 35 Panoptic.

B

#8 Mike B

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Posted 18 October 2005 - 06:35 PM

All things being equal (and they usually aren't ;)), maximize the FOV while also maximizing the magnification. Otherwise you're seein' the same field, just less magnified, and with a larger exit-pupil. However quality of lenses, coatings, design & implementation, eye-relief, AFOV & it's ergonomics, & price seem like they're all variables that folks go one way or the other on... :question:

Bottom line- there's a lot of really nice stuff out there that, especially if you're using a longer FL animal, you won't need to spend a small fortune on.
Unless you want to :lol:
:cool: mike b

#9 RGM

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Posted 18 October 2005 - 07:02 PM

I use the Pan 35mm. Great EP, but expensive. At f10, there are other EPs that should work well for a lot less money. Some have already been mentioned.

#10 snorkler

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Posted 18 October 2005 - 08:15 PM

No one has discussed the .63 focal reducer. It lowers the focal length of your 8" SCT from 2000 mm to 1260 mm. That, in turn, increases your field of view from 1.1 degrees (at 59X) to 1.72 degrees (at 37X) with a 35 mm Panoptic, from 1.18 degrees (at 66X) to 1.87 degrees (at 42X) with a 31 mm Nagler, and from 1.3 degrees (at 49X) to 2.11 degrees (at 31X) with a 42 mm GSO. The 42 mm GSO with 65 degree AFOV has a 6.7 mm exit pupil with the focal reducer. That's about the widest you can go without the exit pupil getting too large.

For comparison, your 30mm Ultima gives a .73 degree field of view at 68X at 2000/10, and a 1.16 degree fov at 43X at 1260/6.3. Any of the widefield eyepieces beat those figures easily, but the GSO 42 gives you the widest field. If you play with the figures, you can see that you can have the same 66X magnification you now get, but with a 1.18 degree field that's more than 150% of your present fov, by simply buying a 31 Nagler. But when you're trying to get whole portions of the Veil Nebula or the entire Double Cluster in your fov, you want the focal reducer and the GSO 42 (or something similar).


Photographically, the focal reducer vignettes your image, but I haven't noticed much of a problem visually when focusing and framing. I use small flip mirrors for astrophotography, so can't say how your image would look in a real 2" diagonal.

#11 Guest_**DONOTDELETE**_*

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Posted 18 October 2005 - 10:29 PM

Thanks for you help everyone! Are there any favorites in the best bang for the buck category? The GSO 42 seems to be coming up a lot in the discussion. Are those who own this happy with it? Where's the best place to get one online? I guess I'm a little leery of buying an EP the size of a coke can with the price of a bottle of Dom Perignon unless it will truly make a dramatic difference with an f/10 SCT

#12 snorkler

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Posted 19 October 2005 - 01:00 AM

Steve,

Read here and here for discussions of the 42 mm GSO Superwide. Since you'll be using it on an f/10 or f/6.3 scope, it should do well for your needs.

You can pick one up for $60-70 from Owl Services, DBA, Skywatcher (ultra wide), Agena, and others. Do a search for 42mm GSO or 42mm superwide.

I'm happy with mine, but I bought it as a public star party eyepiece.

#13 Rich N

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Posted 19 October 2005 - 01:13 AM

The central obstruction of your telescope can be a problem with very low powers. If you want lower power buy a shorter focal length telescope.

I suggest a fine refractor.

All the best,
Rich

#14 snorkler

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Posted 19 October 2005 - 07:31 AM

I should mention that used Pentax XL40s come up for sale from time to time in the $225 range. They're nearly 4 times the cost of the GSO 42, but nobody questions their quality. From edge to edge they're comparable to Televue Panoptics and Naglers, and a lot cheaper.

#15 Mike B

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Posted 19 October 2005 - 12:14 PM

Steve-
Rich is correct on the CO & it's limitations on your scopes low power FOV. Also, i'm not sure where vignetting due to physical constraints (baffle/focuser tube) comes in... but i've always heard that the FR & 1.25" EP route will only match & not exceed the 2" WA EP route, and that 2" WA EPs & the FR don't mix too well. Haven't tried it, so i can't say for sure.

Also, is your 2" diagonal an SCT thread-on type, or a full 2" refractor type & inserted into a 2" SCT visual back. If the former, you may encounter vignetting from the throttled-down field neck on that type of diagonal. Mine uses the latter type, so again, i ain't tried so can't say for sure. Someone here will know. :grin:
:cool: mike b

#16 sixela

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Posted 19 October 2005 - 02:19 PM

No one has discussed the .63 focal reducer.


If you install it, anything larger than a Pan 24 will start to vignette (which makes a 2" diagonal really unnecessary, at least if you always plan to use the focal reducer).

Considerations about exit pupils aren't that important if the baffle tube in the SCT and the clear aperture of the focal reducer vignette before your eye's pupil does ;).

#17 Guest_**DONOTDELETE**_*

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Posted 19 October 2005 - 03:42 PM

Thanks again everyone! I ordered a GSO 42 from Agena. How can I go wrong for $60? I'll save the focal reducer for when I decide to get into astrophotography.

Mike, I'm using a Williams dielectric 2 inch diagonal attached to the back of the Meade microfocuser. I'm hoping that this combination doesn't result in vignetting. I'll report back when I get the eyepiece.

Rich, I'm still in the early compound telescope phase of my astronomical life.... I haven't graduated to the fine refractor stage yet! ;)

#18 Jeff Young

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Posted 19 October 2005 - 04:03 PM

I did quite a bit of research before buying a wide field eyepiece for my 8" LX200GPS. I was aware that the central baffle tube would *slightly* vignette a 68° 35mm Panoptic, but probably not too noticably. However, I aslo planned on getting a bigger scope sometime in the future, which would handle a Panoptic 41, and I felt the 35 would be a bit too close in focal length. So I ended up getting a 27mm Panoptic as my wide-field eyepiece (_great_ eyepiece, by the way).

Fast forward a bit. Suffering from aperture fever, I plunk down for a larger scope and a Pan 41. I keep the 8" as a portable scope. Now, not having my observatory done yet, and therefore having nowhere to mount the larger scope, I'm out observing with the 8". And there sits a Panoptic 41. Well, hey, we'd better give it a go, huh?

Now, I didn't do any rigorous limiting magnitude tests, but I have to say that the vignetting (which I'm sure was there) was _not_ casually noticable. A bit more than that really: I spent some time _looking_ for it and couldn't detect it. As star slowly slewed to the outside did _not_ appear to noticably dim.

Go figure....

-- Jeff.

#19 snorkler

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Posted 20 October 2005 - 05:35 PM

Rich, I'm still in the early compound telescope phase of my astronomical life.... I haven't graduated to the fine refractor stage yet! ;)


Remember, you're in a CAT forum. Many of us believe refractor people graduate up to CATs, not v.v. :jump:

#20 Jeff Young

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Posted 21 October 2005 - 05:32 AM

Remember, you're in a CAT forum. Many of us believe refractor people graduate up to CATs, not v.v. :jump:


Indeed (or at least a Newt or Dob).

Someday they'll all trade in their little cups for a proper bucket. :smirk:

-- Jeff.

#21 Guest_**DONOTDELETE**_*

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Posted 21 October 2005 - 08:52 AM

As long at this topic remains so active, I'd like to explore the OTHER end of the EP spectrum. Are there any recommendations for a HIGH power eyepiece focal length and type? For a night with average seeing (in the frequently hazy midwest), is 10 mm (200x with my 8 inch f/10 SCT) about the optimal high power focal length to use? Do you have any favorites? Is a Tele Vue Radian (at $240) worth the expense? Are there good lower cost alternatives?

And since this IS a CAT forum, nobody bring up the "R" word please :shameonyou:

#22 snorkler

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Posted 21 October 2005 - 10:08 AM

Yes, 10 mm is probably close to the upper magnification limit for your seeing conditions. There will be rare nights when you can Barlow your 10 mm and go to 400X, but I'll bet you can count those on the fingers of one hand over a year's time.

Ditto for 300X, which is where a 7 mm eyepiece will take you. So 10 mm is about right. If you yearn for a better eyepiece, the TV Radians are good, but I personally prefer a used Pentax 10.5 XL. Some Radians show color fringing and kidney-beaning - and their adjustable eyecup click stops have stopped my heart more than once as the eyepiece started dropping at the speed of gravity while I gripped the eyepiece cup so hard I could dent the metal!

For a cheap-bucks option, maybe the GSO 9 mm ultrawide. As with the GSO 42 mm, you've only got $50 or so to lose. It'll be better than a standard 10 mm Plossl.

#23 Guest_**DONOTDELETE**_*

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Posted 21 October 2005 - 11:30 AM

Thanks for the advice Darrell. Apparently the Pentax XL line has been replaced by the XW line. Do you have any experience with the 10 XW if I decide to not go the cheap-bucks route?

Steve

#24 Mike B

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Posted 21 October 2005 - 11:38 AM

Hi Steve-

The Orion "Hilight" & "Ultrascopic" 10mm Ploessls are pretty highyly regarded. I think the Antares unit is similar, if not identical to the Ultrascopic. The Vixen LVL 9mm, which i have personally- gives excellent views! It may be one of the sweetest of that series. Plus it has 20mm of ER, so i really enjoy using it while wearing glasses... don't know if that's an issue for you. UO has a 9mm Orthoscopic which will be tough to beat, price or performance... and there's always the 9mm Nagler!

A person could also look into a couple of high quality barlows- say 2x & 2.8x (UO "Klee"?)- to use with longer FL EPs to reach up to those higher mags... ie. a 25mm EP would function as a 12.5mm EP with the 2x barlow, and as a 9mm with the 2.8 barlow! And a 25mm EP is a lot easier to view thru...

Cheers,
:cool: mike b

#25 Jeff Young

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Posted 21 October 2005 - 01:39 PM

Personally, I still like a wide field of view at 200x. There are a lot of DSOs (globulars and planetaries mostly) which you'll want this level of magnification for. I'd go for a Nagler 11 T6.

At even higher powers, I don't like to spend that kind of money for something that only comes out of the kit every now and again, and pretty much only for planets which don't require the larger FOV. So a couple of UO orthos, Tak LEs, or the like at around 8 and 5 might fit the bill. (Or, if you've got a barlow, you can just barlow the Nagler and your next-longer focal length occular.)

But be forewarned: Darrell was spot-on -- you *really* may only get to use the 5 a couple of times a year. On the other hand, when you do (like I did on Mars last week), it'll pay for itself in about 15 minutes. Wow, what a view!

-- Jeff.


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